I wanted to setup a shopify store front and send out stupid meme related postcards or anything of that matter. In return send bitcoins at market price

postcard-30$ profit 28$
I would pay the 2.9%+.30cents
28$-2.9%-.30cents=$26.92profit

shopify would provide security for debit card transactions
and i can validate shipping so people couldn't try to gain bitcoins and reverse transactions


any comments or concerns you think i would encounter?